3 ms·

In what sense does x: float = 1.0 instantiate?

• blattimwind 8y ago
  List[Tuple[Tuple[str, int], Dict[str, str]]] creates a bunch of objects; if you're having a closure these are necessarily created each time the closure is invoked, by evaluating the entire "List[Tuple[Tuple[str, int], Dict[str, str]]]" expression.
  • marmaduke 8y ago
    Why can’t you close over that type instantied outside the closure? Complicated closures are often more idiomatically as classes where the aggregate type would be a class member.
    • blattimwind 8y ago
      There are two cases to consider. One is where the closure is called multiple times. This is the "by necessity" case, because the enclosed definition is executable and Python must make believe that this definition is re-executed every time the function is called. If you are just calling the enclosed function then of course this does not happen. Compare: def mytype(): print("!") return dict() def closure(): def enclosed(x: mytype()): pass return enclosed print("Calling the closure") for i in range(10): closure() print("Calling the enclosed") f = closure() for i in range(10): f(0) Note that using closures is almost always faster in Python than classes, because accesses to enclosed variables are done through offsets instead of attribute lookup (this gap has been somewhat closed, but is still significant in some cases; arguably almost all of these cases indicate that you are using either the wrong language, or the wrong implementation). So adding overhead to closures can be a somewhat valid reason to avoid using these annotations.